1. Field of the Invention
The present invention is directed to nonwoven fabrics useful for a wide variety of applications. Such nonwovens in the form of lightweight, soft porous webs are used as cover liners for personal care products such as sanitary napkins and disposable diapers, for example. Other embodiments of nonwovens having engineered capillary structures are useful, for example, as intermediate transfer layers for such personal care products acting to distribute fluids and minimize leakage. Still others, frequently in heavier basis weights, are highly absorbent and serve as the absorbent medium for personal care products. In addition to nonwovens for personal care applications the field of the invention embraces nonwovens for many other uses, for example in the household as cleaning materials and wipers, in the service product area as towels, bathmats and the like, in the automative and marine areas for scrubbing, wiping, protective and other uses and in the hospital and veterinary areas as wipes and applicators. The field includes nonwoven fabrics broadly for these and many other uses which will be apparent in light of the description below, and preferred embodiments of will be set forth hereinafter in detail. Moreover, the field embraces methods and apparatus for manufacturing such nonwovens resulting in engineered, three-dimensionally structured webs.
2. Description of the Prior Art
The manufacture of nonwoven fabrics is a highly developed art. In general, nonwoven webs and their manufacture involve forming filaments or fibers and depositing them on a carrier in such manner so as to cause the filaments or fibers to overlap or entangle as a mat of a desired basis weight. The bonding of such a mat may be achieved simply by entanglement or by other means such as adhesive, application of heat and/or pressure to thermally responsive fibers, or, in some cases, by pressure alone. While many variations within this general description are known, two commonly used processes are defined as spunbonding and meltblowing. Spunbonded nonwoven structures are defined in numerous patents including, for example, U.S. Pat. No. 3,565,729 to Hartmann dated Feb. 23, 1971, U.S. Pat. No. 4,405,297 to Appel and Morman dated Sept. 20, 1983, and U.S. Pat. No. 3,692,618 to Dorschner, Carduck, and Storkebaum dated Sept. 19, 1972. Discussion of the meltblowing process may also be found in a wide variety of sources including, for example, an article entitled, "Superfine Thermoplastic Fibers" by Wendt in Industrial and Engineering Chemistry, Volume 48, No. 8, (1956) pages 1342-1346 as well as U.S. Pat. No. 3,978,185 to Buntin, Keller and Harding dated Aug. 31, 1976, U.S. Pat. No. 3,795,571 to Prentice dated Mar. 5, 1974, and U.S. Pat. No. 3,811,957 to Buntin dated May 21, 1974. Spunbonded webs and meltblown webs are widely used for many applications, including personal care products as described, for example, in U.S. Pat. No. 4,397,644 to Matthews, Allison, Woon, Stevens, and Bornslaeger, dated Aug. 9, 1983 or U.S. Pat. No. 4,372,312 to Fendler and Bernardin dated Feb. 8, 1983. Other nonwoven manufacturing processes include carding, wetlaying and needing, but the invention will be described with particular reference to meltblown and spunbonded webs which represent preferred embodiments.
In addition to processes for making nonwovens, in general, it is known to form nonwoven fabrics, broadly, into so-called "three-dimensional" configurations that result in a web having a base plane but wherein fibers project out of the base plane in one, several or many different forms. For example, U.S. Pat. No. 4,103,058 to Humlicek dated July 25, 1978 describes a pillowed web of meltblown microfibers where a pattern of pillowed low density regions is separated by high density areas formed by collecting on a perforated screen. U.S. Pat. No. 4,041,951 to Sanford dated Aug. 16, 1977 describes a nonwoven web containing a multiplicity of depressed areas providing wet resilience in a diaper top sheet that tends to isolate the wearer's skin from moisture contained in the absorbent layer. U.S. Pat. No. 3,240,657 to Hynek dated Mar. 15, 1966 describes an apertured web wherein the perforations are formed between relative low density web areas. Various forming techniques for making matting structures are described in prior art patents such as U.S. Pat. No. RE31,599 to Rasen, Vollbrecht and Schenesse dated June 12, 1984 which discusses forming on a variety of surfaces having projections of different types and U.S. Pat. No. 4,488,928 to Kon and Schmidt dated Dec. 18, 1984 which discusses the use of vacuum drawing fibers onto various wire or belt forming surfaces.
Notwithstanding the intense investigation into the subject, there remains desired a nonwoven fabric that can be produced with widely varying, but carefully controlled, properties such as permeability, bulk, absorbency, liquid transmission, flexibility or stiffness, and density.